package leetcode.editor.cn;

//给定一个 m x n 二维字符网格 board 和一个字符串单词 word 。如果 word 存在于网格中，返回 true ；否则，返回 false 。 
//
// 单词必须按照字母顺序，通过相邻的单元格内的字母构成，其中“相邻”单元格是那些水平相邻或垂直相邻的单元格。同一个单元格内的字母不允许被重复使用。 
//
// 
//
// 示例 1： 
//
// 
//输入：board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = 
//"ABCCED"
//输出：true
// 
//
// 示例 2： 
//
// 
//输入：board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = 
//"SEE"
//输出：true
// 
//
// 示例 3： 
//
// 
//输入：board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = 
//"ABCB"
//输出：false
// 
//
// 
//
// 提示： 
//
// 
// m == board.length 
// n = board[i].length 
// 1 <= m, n <= 6 
// 1 <= word.length <= 15 
// board 和 word 仅由大小写英文字母组成 
// 
//
// 
//
// 进阶：你可以使用搜索剪枝的技术来优化解决方案，使其在 board 更大的情况下可以更快解决问题？ 
// Related Topics 数组 回溯 矩阵 👍 1283 👎 0

//Java：【79】 - 单词搜索
public class WordSearch_79{
    public static void main(String[] args) {
        Solution solution = new WordSearch_79().new Solution();
                // TO TEST
    }
    
    //leetcode submit region begin(Prohibit modification and deletion)
class Solution {
        int[] dx = new int[]{1,0,-1,0};
        int[] dy = new int[]{0,1,0,-1};
    public boolean exist(char[][] board, String word) {
        boolean[][] visited = new boolean[board.length][board[0].length];
        for (int i = 0; i < board.length; i++) {
            for (int j = 0; j < board[0].length; j++) {
                if(next(board, word, visited, i,j,0))
                    return true;
            }
        }
        return false;
    }

    public boolean next(char[][] board, String word, boolean[][] visited, int x, int y, int index){
        boolean flag = false;
        if(index>=word.length()) return true;
        if(x<0 || x>= board.length || y<0 || y>=board[0].length || board[x][y]!=word.charAt(index) || visited[x][y]) return flag;
        visited[x][y] = true;
        for (int k = 0; k < 4; k++) {
            flag = flag || next(board, word, visited, x+dx[k], y+dy[k], index+1);
        }
        visited[x][y] = false; // 回退到上一个字符，那么该位置就要撤销访问
        return flag;
    }
}
//leetcode submit region end(Prohibit modification and deletion)

}
